1. Field of the Invention
The present invention pertains to the storage of information, and particularly to automated cartridge handling systems such as cartridge libraries which store cartridges or cassettes of magnetic tape.
2. Related Art and Other Considerations
The economic and compact storage of information is increasingly important in the computer industry, particularly so as the computer unleashes new potentials in numerous fields such as audio visual and/or multimedia.
In the early days of computers, information requiring storage could be transmitted from a computer to a tape drive, whereat the information was magnetically recorded on or read from a large reel of tape. Upon completion of an operation of recording on the tape, for example, the reel would be removed manually from the tape drive and mounted in a rack. Another reel from the rack could then be manually mounted, if necessary, in the drive for either an input (tape reading) or output (recording to tape) operation.
Eventually it became popular to enclose magnetic tape in a cartridge, the cartridge being considerably smaller than the traditional tape reels. While many persons are familiar with tape cartridges of a type which can be loaded into a "tape deck" for reproduction of audio information (e.g., music), it is not as commonly realized that similar cartridges, although of differing sizes, can be used to store such information as computer data. For years now magnetic tape cartridges have proven to be an efficient and effective medium for data storage, including but not limited to computer back-up.
Large computer systems have need to access numerous cartridges. To this end, automated cartridge handling systems or libraries for cartridges have been proposed for making the cartridges automatically available to the computer. Many of these automated libraries resemble juke boxes. Typically, prior art automated cartridge libraries have an array of storage positions for cartridges, one or more tape drives, and some type of automated changer or cartridge engagement/transport mechanism for picking or gripping a cartridge and moving the cartridge between a storage position and the tape drive.
The following U.S. patents, all commonly assigned herewith and incorporated herein by reference, disclose various configurations of automated cartridge libraries, as well as subcomponents thereof (including cartridge engagement/transport mechanisms and storage racks for housing cartridges):
U.S. Pat. No. 4,984,106 to Herger et al., entitled "CARTRIDGE LIBRARY SYSTEM AND METHOD OF OPERATION THEREOF"; PA1 U.S. Pat. No. 4,972,277 to Sills et al., entitled "CARTRIDGE TRANSPORT ASSEMBLY AND METHOD OF OPERATION THEREOF"; PA1 U.S. Pat. No. 5,059,772 to Younglove, entitled "READING METHOD AND APPARATUS FOR CARTRIDGE LIBRARY"; PA1 U.S. Pat. No. 5,103,986 to Marlowe, entitled "CARTRIDGE RACK"; and, PA1 U.S. Pat. Nos. 5,237,467 and 5,416,653 to Marlowe, entitled "CARTRIDGE HANDLING APPARATUS AND METHOD WITH MOTION-RESPONSIVE EJECTION". PA1 U.S. Pat. No. 5,498,116 to Woodruff et al., entitled "ENTRY-EXIT PORT FOR CARTRIDGE LIBRARY". PA1 U.S. Pat. No. 5,487,579 to Woodruff et al., entitled "PICKER MECHANISM FOR DATA CARTRIDGES".
U.S. Pat. No. 5,059,772 to Younglove discloses a cartridge library wherein the cartridge magazines each have a reflective indicia used for precise placement of the magazine.
U.S. Pat. No. 5,661,287 to Schaefer et al. ("Schaefer") discloses a single laser light source in combination with a single reflectivity sensor for multiple sensing and calibration functions for a storage library subsystem. In Schaefer, a rotatable carousel has an "L-shaped" white target positioned at two joining edges of a void path on the edge of the carousel. Once the single laser light source and single reflectivity sensor have been employed to determine coordinates of the L-shaped target, the position of removable magazines relative to the L-shaped target are determined in view of known offsets. Thus, Schaefer does not separately sense the position of each magazine, but instead makes an estimation thereof based on expected offset from the L-shaped target and certain tolerances. In fact, the position of all of Schaefer's library components are estimated in view of fixed offsets from the target. However, as Schaefer acknowledges, there is variance in the seating of magazines within the library as well as other library tolerances. Accordingly, Schaefer's uni-target-based positioning requires that Schaefer provide various compensation measures when problems are encountered during operation of the cartridge gripper mechanism, as set forth in U.S. Pat. No. 5,661,287 to Schaefer et al. Moreover, Schaefer employs the same single reflectivity sensor both to sensing the presence of a cartridge, and to perform other functions such as calibration and cartridge barcode reading. Schaefer employs a single reflectivity sensor which monitors only a single location. Among its other problems, usage of the same reflectivity sensor does not allow Schaefer to distinguish between absence of a magazine and absence of a cartridge in the magazine. Further, Schaefer requires a label on every cartridge.
What is needed, therefore, and an object of the present invention, is a cartridge library providing precise component detection and location.